Abstract: Based on the research on the effects of radon exhalation and migration caused by the CO₂ injection, the feasibility is discussed that the application of radon measurement method in CO₂ migration monitoring after gas injection in coal seam. The trend surface analysis method is used to deal with the detection results of radon measurement, the results show that the gas (CO₂) injection fracturing in coal seam, it is beneficial to increase radon emanation coefficient, which makes radon anomalies measurable on the ground. The coal seam direction can affect the CO₂ migration in low metamorphic coal seam, the migration happens easily along the coal seam direction. The radon measurement method with activated carbon spectrum can be used to monitor CO₂ migration after gas injection.